Roblox’s strictness on off-site links seems like it’s for kid-friendliness PR reasons rather than being based on how the sites are actually moderated, since as many others have stated, you are 100% allowed to swear and post certain other content on Twitter/Youtube/Twitch which would not be allowed on Roblox, yet those links are still allowed simply because they’re the big-name sites that everyone knows.
I hope that the group system rework will be placed at a much higher priority if Roblox is going to continue blocking off-site community building tools. Roblox has been hinting at the group rework for over 2 years now, but it keeps getting pushed back again and again. As it stands right now, Roblox groups are a mess, and it’s near impossible to use them to build up a constructive community. Hopefully this time the rework will actually come soon, rather than Soon™. If the on-site tools are finally made good enough, perhaps we will no longer have a need to redirect people to 3rd-party sites.